Here is an
example of a peg failing. If the Bank of England is unsuccessful in enforcing a peg, what makes you think random actors can enforce one? All it takes is one dedicated individual with enough money or a systematic breakdown in confidence across the board.
It's a good job everyone got out of GBP and it was exposed for the scam it was.
Are you saying BTS has a centralized authority that can enforce the continued use of BTS after a major crisis and loss of confidence, until it recovers? That seems to be the only reason people are still 'in' GBP.